Bluetooth wireless technology provides a manner in which many wireless devices may communicate with one another, without connectors, wires or cables. Bluetooth technology uses the free and globally available unlicensed 2.4 GHz Industrial, Scientific, and Medical (ISM) spectrum, for low-power use, allowing two Bluetooth devices within a range of up to 10 to 100 meters to share data with throughput up to 2.1 Mbps. Each Bluetooth device can simultaneously communicate with multiple other devices.
Current common uses for Bluetooth technology include those for headsets, cellular car kits and adapters. Moreover, Bluetooth technology is currently used for connecting a printer, keyboard, or mouse to a personal computer without cables. Since Bluetooth technology can facilitate delivery of large amounts of data, computers may use Bluetooth for connection to the Internet through a mobile phone. Bluetooth devices can connect to form a piconet, which consists of a master and up to seven slave devices. Two types of connections can be established in a piconet: a Synchronous Connection Oriented (SCO) link, and an Asynchronous Connectionless (ACL) link. SCO links provide a circuit-oriented service with constant bandwidth based on a fixed and periodic allocation of time slots that is used for voice transmission. There are also extended synchronous connection-oriented packets (eSCO) that have the same functionality as SCO packets but allow for more packet types, data types, and limited retransmissions. ACL connections, on the other hand, provide a packet-oriented service that is used for transmission of data and control signals. Traditionally, voice communication on SCO is bi-directionally processed by a voice codec or encoder/decoder while stereo communication on ACL is uni-directionally processed by a stereo codec that is encoded by the source and decoded by the sink without an audio return path. In a communication device, there are two separate codecs, one for processing mono audio on SCO and the other for processing stereo audio on ACL.
Wireless Local Area Networks (WLANs) are becoming compatible with many different types of products. While businesses originally installed WLANs so that desktop computers could be used on networks without expensive wiring, the functionality of the WLANs has evolved to allow mobile communication devices, such as wireless telephones, laptop computers, personal digital assistants (PDAs) and digital cameras to connect to WLANs for Internet access and wireless Voice over Internet Protocol (VoIP) telephone service. Short for wireless fidelity, WiFi is a trademark for sets of product compatibility standards for WLANs. Manufacturers of mobile communication devices such as cellular telephones are WiFi enabling the devices so that when a user roams into a WiFi hot spot, a telephone can switch its communication protocol from the cellular band that uses licensed, limited spectrum to WiFi communication protocol that uses available unlicensed spectrum. In indoor situations, a switch to a WiFi protocol from a cellular network such as one based on the Global System for Mobile Communication standard (GSM) may be additionally beneficial since a cellular network can lose its signal strength indoors while a WLAN may have a strong signal within a hotspot.
The Bluetooth 2.4 GHz radio band is close to that of particular transceivers that operate at 2.3 GHz or 2.5 GHz, such as a Worldwide Interoperability for Microwave Access (WiMAX) transceiver based on IEEE 802.16e. Communication of audio signals between Bluetooth devices may collide in time with other signals such as WiFi and other standards-based wireless technologies such as WiMAX, thus desensitizing the receivers due to insufficient blocking performance and overlapping spectrum allocations. There can be adjacent channel interference with WiFi for example and with WiMAX, as the Bluetooth guard band is only 20 MHz. Synchronous connections, in particular SCO, such as those used in headsets are inflexible in scheduling of transmission and reception and result in simultaneous use of both radios, especially in an “802.16e” transceiver on a mobile device having packets scheduled by the WiMAX basestation, causing interference problems. While synchronous connections using eSCO have a limited ability to schedule packet transmissions, due to the limited retransmission window, they will still have periodic collisions with other wireless technologies and use more bandwidth and system resources than SCO links. The Bluetooth Core Specification describes a solution for co-existence with WiFi that mitigates interference. Advanced Frequency Hopping (AFH) is one technique that shrinks the available bandwidth to prevent using the same portion of the ISM band as another technology. However this does not solve the problem of adjacent channel interference from other technologies such as WiMAX with high transmit powers and poor adjacent channel rejection. When Bluetooth and WiFi or WiMAX are collocated, AFH can be insufficient and a collaborative method of co-existence such as Packet Traffic Arbitration (PTA) may be used. However, PTA can significantly impact the WiFi data rate when Bluetooth SCO or eSCO is active.
Bluetooth devices, and particularly headsets, enjoy popularity because they can offer users the ability to communicate while seamlessly operating in different environments. Accordingly, providing improved voice quality over Bluetooth has become important for mobile device manufacturers. It would be beneficial were improvements made to audio quality over Bluetooth.
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